obama says he is skeptical of the claims by the assad regime the rebels are using chemical weapons. he said that would be a game changer and cross a line for the united states. with more on this here's abc's alex marquardt. >> reporter: chaos in the hospital, men, women, children on respirators as family members wailed. in this brutal war this appears to have been a first. a rocket suspected of carrying a chemical slammed into a neighborhood in aleppo held by the syrian army. 25 were killed. over 100 wounded. >> translator: i felt my chest close. i couldn't breathe or speak. this little girl cried. i lost my mother. father and brother. >> reporter: the syrian regime accused the rebels of launching the rocket and called for an international investigation. the rebels blame the regime. israel said there is no doubt chemical weapons were used. but president obama wasn't so quick to agree. >> we intend to investigate thoroughly exactly what happened. >> reporter: it does not appear the chemical in question was one of those most feared in president bashar al-assad's arsenal. mustard gas o